542 Stresses in Wire Rope. :; <<;•: pit-head; and A is thereby caught, being slipped relatively down- ward. The jaws then open or catch on B, as at D. Fig. 554 shews Fowler's travelling crane driven by wire rope round clip pullies. A is the rope arrangement, and the power is distributed for travelling at c c, cross traversing at r>, and lifting at E F. The last is accomplished by the rotation of screw F, which shortens the lifting chain attached to nut E. The arrangement is suitable for very heavy cranes. Cable tramways are useful for bad inclines. An endless rope travels in a conduit A, Fig. 555, and the car carries the gripping lever B, which, when moved to the vertical, raises the rollers c c, and brings the jaws D D together. Some jerk is, of course, unavoidable. Fig. 557 is a towing arrangement adopted on some German canals. A rope is anchored on the canal bottom, and the tug winds itself along by the engine-driven clip pulley. The rope serves as a rail, and with the pulley forms a kinematic pair. In wire-rope transmission the tension ratio is usually 2 : i and the speed 3000 to 6000 feet per m. The stresses in the rope are due to: (1) Weight of rope and the form of hanging curve. (2) Bending of rope round pulley. (3) Centrifugal force. (i) In Fig. 558 the catenaries may be considered as parabolas for all practical purposes. Then the tangent T A being drawn, by bisecting c D at A, the force diagram will give the value of T, in terms of W the weight of rope between the pullies, and B the pressure on the bearing. The weight of wire rope per foot = (1*34 x d*} Ibs. (2) Taking the general bending formulae, El J ^ Bm==_==/ /Z p y and I = Zy where p = radius of pulley, andj' that of the rope-wire: = 30,000,000 —.